mark: export pytest.Mark for typing purposes

The type cannot be constructed directly, but is exported for use in type
annotations, since it is reachable through existing public API.

Author: bluetech

changelog/7469.deprecation.rst

@@ -0,0 +1,5 @@
+Directly constructing the following classes is now deprecated:
+
+- ``_pytest.mark.structures.Mark``
+
+These have always been considered private, but now issue a deprecation warning, which may become a hard error in pytest 7.0.0.

changelog/7469.feature.rst

@@ -0,0 +1,10 @@
+The types of objects used in pytest's API are now exported so they may be used in type annotations.
+
+The newly-exported types are:
+
+- ``pytest.Mark`` for :class:`marks <pytest.Mark>`.
+
+Constructing them directly is not supported; they are only meant for use in type annotations.
+Doing so will emit a deprecation warning, and may become a hard-error in pytest 7.0.
+
+Subclassing them is also not supported. This is not currently enforced at runtime, but is detected by type-checkers such as mypy.

doc/en/reference.rst

@@ -239,7 +239,7 @@ For example:
     def test_function():
         ...
 
-Will create and attach a :class:`Mark <_pytest.mark.structures.Mark>` object to the collected
+Will create and attach a :class:`Mark <pytest.Mark>` object to the collected
 :class:`Item <pytest.Item>`, which can then be accessed by fixtures or hooks with
 :meth:`Node.iter_markers <_pytest.nodes.Node.iter_markers>`. The ``mark`` object will have the following attributes:
 
@@ -863,7 +863,7 @@ MarkGenerator
 Mark
 ~~~~
 
-.. autoclass:: _pytest.mark.structures.Mark
+.. autoclass:: pytest.Mark()
     :members:
 
 

src/_pytest/mark/structures.py

@@ -28,6 +28,7 @@
 from ..compat import NOTSET
 from ..compat import NotSetType
 from _pytest.config import Config
+from _pytest.deprecated import check_ispytest
 from _pytest.outcomes import fail
 from _pytest.warning_types import PytestUnknownMarkWarning
 
@@ -200,21 +201,38 @@ def _for_parametrize(
 
 
 @final
-@attr.s(frozen=True)
+@attr.s(frozen=True, init=False, auto_attribs=True)
 class Mark:
     #: Name of the mark.
-    name = attr.ib(type=str)
+    name: str
     #: Positional arguments of the mark decorator.
-    args = attr.ib(type=Tuple[Any, ...])
+    args: Tuple[Any, ...]
     #: Keyword arguments of the mark decorator.
-    kwargs = attr.ib(type=Mapping[str, Any])
+    kwargs: Mapping[str, Any]
 
     #: Source Mark for ids with parametrize Marks.
-    _param_ids_from = attr.ib(type=Optional["Mark"], default=None, repr=False)
+    _param_ids_from: Optional["Mark"] = attr.ib(default=None, repr=False)
     #: Resolved/generated ids with parametrize Marks.
-    _param_ids_generated = attr.ib(
-        type=Optional[Sequence[str]], default=None, repr=False
-    )
+    _param_ids_generated: Optional[Sequence[str]] = attr.ib(default=None, repr=False)
+
+    def __init__(
+        self,
+        name: str,
+        args: Tuple[Any, ...],
+        kwargs: Mapping[str, Any],
+        param_ids_from: Optional["Mark"] = None,
+        param_ids_generated: Optional[Sequence[str]] = None,
+        *,
+        _ispytest: bool = False,
+    ) -> None:
+        """:meta private:"""
+        check_ispytest(_ispytest)
+        # Weirdness to bypass frozen=True.
+        object.__setattr__(self, "name", name)
+        object.__setattr__(self, "args", args)
+        object.__setattr__(self, "kwargs", kwargs)
+        object.__setattr__(self, "_param_ids_from", param_ids_from)
+        object.__setattr__(self, "_param_ids_generated", param_ids_generated)
 
     def _has_param_ids(self) -> bool:
         return "ids" in self.kwargs or len(self.args) >= 4
@@ -243,6 +261,7 @@ def combined_with(self, other: "Mark") -> "Mark":
             self.args + other.args,
             dict(self.kwargs, **other.kwargs),
             param_ids_from=param_ids_from,
+            _ispytest=True,
         )
 
 
@@ -320,7 +339,7 @@ def with_args(self, *args: object, **kwargs: object) -> "MarkDecorator":
 
         :rtype: MarkDecorator
         """
-        mark = Mark(self.name, args, kwargs)
+        mark = Mark(self.name, args, kwargs, _ispytest=True)
         return self.__class__(self.mark.combined_with(mark))
 
     # Type ignored because the overloads overlap with an incompatible
@@ -515,7 +534,7 @@ def __getattr__(self, name: str) -> MarkDecorator:
                     2,
                 )
 
-        return MarkDecorator(Mark(name, (), {}))
+        return MarkDecorator(Mark(name, (), {}, _ispytest=True))
 
 
 MARK_GEN = MarkGenerator()

src/pytest/__init__.py

@@ -21,6 +21,7 @@
 from _pytest.freeze_support import freeze_includes
 from _pytest.logging import LogCaptureFixture
 from _pytest.main import Session
+from _pytest.mark import Mark
 from _pytest.mark import MARK_GEN as mark
 from _pytest.mark import param
 from _pytest.monkeypatch import MonkeyPatch
@@ -89,6 +90,7 @@
     "LogCaptureFixture",
     "main",
     "mark",
+    "Mark",
     "Module",
     "MonkeyPatch",
     "Package",